"Have you tried cleaning it with the TV on? So that it might warm up a bit and be easier to wipe off (and if your tv doesn't heat up [do tv heat up? I haven't been near one in ages] maybe a quick blast of hair dryer)."
If it's a flat panel TV, it won't generate an appreciable amount of heat when it's on, and it's a bad idea to try heating it with a hair dryer because spot heat like that can damage it. One way to clean it is to use monitor wipes, but be aware that it'll take a gentle hand, a lot of time and a fair number of wipes to get crayon residue off the screen. Isopropyl alcohol in water will also work, as long as you use a microfiber cloth or the like. Don't bear down on the surface and don't "scrub" it hard, and eventually it'll come clean. Be sure to power down the TV and unplug it before trying this, and above all, Be. Patient.